Amnesty International urged Qatar to end abuse of migrants working on football World Cup infrastructure, as it issued a report Monday citing cases in which they were referred to as "animals".
The 169-page report called on world football governing body FIFA to press the Gulf state to improve labour conditions, alleging "alarming" levels of exploitation against the workers, mostly from South or Southeast Asia.
Doha, which rejects claims of slavery-style conditions on its construction sites in the world's wealthiest nation per capita, said it would investigate the report's findings.
Amnesty said its researchers had heard one construction firm manager use the term "animals" to describe migrant workers.
And a worker told the watchdog that "Nepalis are treated like cattle".
Amnesty secretary general Salil Shetty said the findings indicated "an alarming level of exploitation" in Qatar, and called the abuses "widespread" and "not isolated".
"FIFA has a duty to send a strong public message that it will not tolerate human rights abuses on construction projects related to the World Cup."
After meeting Qatar's emir and prime minister on November 9 in Doha, FIFA chief Sepp Blatter said the issue of working conditions was being addressed.
On Monday, FIFA said human rights must be respected.
"FIFA has made very clear... that it upholds the respect for human rights and the application of international norms of behaviour as a principle and part of all our activities," it said in a statement.
It said that it understood and shared Amnesty's efforts to ensure justice and respect for rights, adding it expects "the hosts of its competitions fully respect these".
German trade union chief Michael Sommer, meanwhile, called for FIFA to pull the World Cup from Qatar unless the country improves conditions of migrant workers.
"We urge an immediate end to forced labour conditions or the World Cup be withdrawn from Qatar," said the president of the Federation of German Trade Unions (DGB), Michael Sommer.
Shetty said Amnesty had met Qatari officials who were "very willing to recognise that there is a problem and... strongly oriented to find solutions".
After embarking on a multi-billion-dollar plan to host the 2022 World Cup, Qatar has come under the spotlight as migrant workers pour into the tiny gas-rich nation.
The plight of migrant workers remains an issue across the oil-rich Gulf.
Amnesty's report documented several abuses, including "non-payment of wages, harsh and dangerous working conditions, and shocking standards of accommodation".
It said "dozens" of workers have been trapped inside Qatar, which demands foreigners obtain an exit permit to leave.
Qatar to probe findings
In response, Qatar said it would ensure the report was included in an inquiry it has already launched.
The authorities had "asked international law firm DLA Piper to include the Amnesty report... in the independent review it is carrying out concerning the conditions of foreign labour," said a foreign ministry source.
"The state of Qatar gives huge importance to the protection and upholding of human rights by enacting the relevant laws and establishing the bodies tasked with protecting and reinforcing those rights."
Amnesty said "the onus" was on Qatar to change its legislation and to enforce worker protections.
Abuses were systematic under a sponsorship system that "affords unscrupulous employers powers to exploit their employees, not least of which is the ability to prevent workers leaving the country".
Shetty said his team in Doha met "a group of 70 workers" from Nepal, Sri Lanka and other nationalities who said they "have not been paid for nine to 10 months".
"It is simply inexcusable in one of the richest countries in the world that so many migrant workers are being ruthlessly exploited, deprived of their pay and left struggling to survive."
Many workers have also reported poor health and safety standards.
Amnesty cited a Doha hospital representative as saying that "more than 1,000 people were admitted to the trauma unit in 2012 (after) having fallen from height at work".
Some 10 percent became disabled and "the mortality rate was 'significant'."
A September report in Britain's Guardian newspaper said 44 Nepalis have died working in Qatar this year.
"Unless critical, far-reaching steps are taken immediately, hundreds of thousands of migrant workers who will be recruited in the coming years to deliver Qatar's vision face a high risk of being abused," Shetty warned.